1. Field of the Invention
This invention relates to magnetic recording and more particularly, to magnetic recording media in the form of tapes and disks for video, audio and computer services.
2. Description of the Prior Art
Magnetic recording mediums such as video tapes have been extensively studied and developed and thus, the electromagnetic characteristics of the mediums have been drastically improved.
As is known in the art, the electromagnetic characteristics have generally a close relation with the smoothness of a support for the magnetic recording medium. Accordingly, it is usual to use a smooth support in order to improve the electromagnetic characteristics.
However, a magnetic recording medium having a smooth base film on which a magnetic recording layer is formed is disadvantageous in that it becomes poor in wear resistance and poor in travelling performance.
In order to overcome the above disadvantage, there have been proposed magnetic recording media which have a back coat layer on a side of a base film opposite to the side on which the magnetic recording layer is formed. The back coat layer generally contains carbon black and non-magnetic particles dispersed in a resin binder. Carbon black is able to prevent the medium from being electrostatically charged. As a consequence, the medium is prevented from deposition of dust thereon and from disturbance in winding. The non-magnetic particles can improve the wear resistance and durability of the medium.
However, we found that the back coat layer comprising carbon black and non-magnetic particles could not work as desired and did not thus improve the characteristics of the medium satisfactorily.
For instance, carbon black has relatively poor dispersability as is known in the art. If carbon black is not adequately dispersed in a coating paint, it tends to agglomerate into lumps. When the paint containing the agglomerates is coated on a support, the resulting back coat layer has very poor surface properties. The magnetic tape having the back coat layer is disadvantageous in that when the tape is rolled, the back coat layer is partially transferred to the surface of the magnetic layer, thus bringing about a lowering of electromagnetic characteristics.
Moreover, non-magnetic particles ordinarily used in combination with carbon black are particles of alumina or chromium oxide. These particles are so hard that members of a magnetic recording and reproducing apparatus which are in contact with the back coat layer in travelling operations are liable to be frictionally abraded with the particles in the back coat layer. This will cause the travelling performance to lower.